It is known that highly purified proteins are time-unstable and are stabilized, for instance, in admixture with saccharides, such as lactose and mannitol, or else with proteins and aminoacids, such as albumin and glycine. Other high-molecular-weight compounds, having a biological origin, as, for instance, the marine colloids, dextran and other polysaccharides and the phospholipids often work equally well. Anyway, since the gonadotropins of the present invention are administered parenterally, these excipients are not suited for an injectable composition because of their allergenicity or their insufficient solubility, in some cases because of their potential toxicity or a concourse of these effects.
The composition of lyophilised proteins is described in M. J. Pikal, BioPharm, October 1990, 25-30. There are reported examples of proteins, such as growth hormone and ribonuclease A, formulated by using stabilizing excipients such as mannitol, glycin, arginine and lactose.
In particular, the lyophilisation is described of proteins in the presence of various substances in their amorphous state, as sugars, which increase the collapse temperature and possible to obtain shorter lyophilisation times. However, it is not feasible, according to the author, to foresee a standard formulation for all the proteins, and the choice of the best formulation requires a remarkable selection work.
German patent DE 3520228 describes bioactive proteins such as lymphokines, interferons, TNF (Tumor Necrosis Factor), insulin, growth hormone, in formulations which are stabilized by means of polysaccharides comprising repetitive maltotriose units. The use of sucrose as a stabilizing agent is known, for instance, in a formulation of lyophilized orgotein, as described in U.S. Pat. No. 3,637,640. International patent application WO 89/10407 describes the formulation with sucrose of M-CSF (Macrophage-Colony Stimulating Factor); patent application WO 89/09610 describes, instead, formulations of TNF which have been stabilized with albumin, dextran, polyethylene glycol, 80 polysorbate PVP, lactose, trialose or even sucrose.
The injectable formulations of gonadotropins are obtained by a process which includes their lyophilisation in order to obtain a dry powder. Gonadotropins are highly liable to denaturization during the lyophilisation process and it is desirable to obtain stable formulations able to maintain a longer cycle life when they are stored at room temperature.
European Patent EP 448146 describes lyophilised gonadotropin containing preparations, which are stabilized by means of a dicarboxylic acid salt, as, for instance, citric acid, tartaric acid and aspartic acid. Gonadotropins which are found on the market are stabilized by means of saccharides, for instance hCG is stabilized by means of mannitol (Profasi.RTM., SERONO) and FSH is stabilized by means of lactose (Metrodin.RTM., SERONO).